1. Field of the Invention
This invention relates to a printing device with at least one transfer roller having a surface that can be charged at least partially with a coating material, for example toner, wherein the coating material can be applied indirectly or directly to a carrier surface of a transfer element.
This invention also relates to a printing method wherein a coating is applied to a workpiece using a transfer element.
2. Description of Related Art
A coating method is known from European Patent Reference EP 0 647 885 A1, which is used for imprinting ceramic and glass products. A toner is employed, with toner particles that have a pigment core, the toner particles consisting of ceramic pigments and glassy flux surrounded by a binder resin envelope. Charge control means are coupled to the binder resin envelope. The toner particles are applied to a paper coated with gum arabic with the aid of an electrostatic copying process. A clear lacquer is applied to the coated paper for fixation. The paper can subsequently be placed on a workpiece to be coated, such as a ceramic or glass product, and can be moistened. The paper used as the transfer means can be pulled off, while the gum arabic layer and the colored coating applied to it adhere to the workpiece.
A firing process is performed at the end, wherein the ceramic coloring melts together with the surface of the ceramic or glass product. With this method it is possible to create high quality and scratch-proof coatings.
Furthermore, a printing device is known from European Patent References EP-OS 0 834 784 and EP-OS 0 727 778, which has a tape-like transfer device with a flexible tape with a silicon coating. This tape is pressed against the workpiece by a roller in the area of the transfer of the toner, however, a coating of two-dimensional surfaces is not possible.
It is one object of this invention to provide a coating device, or a coating method, by which it is possible in a simple way to also coat three-dimensional surfaces in particular, which are curved in space.
The object is achieved with a transfer element that has an expansion element forming the carrier surface, and the carrier surface can be expanded by an expansion device.
The expansion element can be deformed with the expansion device so that it is adapted to the contour of the surface to be imprinted. In a simple way it is possible to also imprint complex courses of three-dimensionally shaped surfaces.
For example, the printing method, or the printing device, is suitable for workpieces made of glass, glass ceramics, ceramics, or plastic which are deformed out of the plane. In particular, three-dimensionally shaped parts are now made of the above mentioned materials and cannot easily be printed cost-effectively by known screen-printing techniques. It is possible with the printing method, or the printing device, to imprint three-dimensionally deformed glass panels, for example curved front panels of ovens, operating panels made of glass, glass doors for furniture or curved architectural glass, three-dimensionally deformed cooking surfaces made of glass ceramics with, for example, lower located cooking areas, or higher located operating areas formed out of the plane, as well as curved fireplace viewing panels, three-dimensionally deformed ceramic parts, for example tableware pieces such as plates and dishes, and three-dimensionally deformed plastic surfaces.
In one embodiment of this invention the transfer element is designed as an endless revolving tape, which has along its longitudinal extension at least partially expansion elements, or is designed as an expansion element itself.
The endless tape allows a continuous efficient coating of workpieces. Thus the transfer element is embodied as a rubber tape.
For example, the printing device can be designed so that the expansion device has a die, the die has a die face which is embodied so that it is matched to the surface to be imprinted of the workpiece. The carrier surface of the expansion element can be pushed out of its expanded initial position against the surface to be imprinted by the die. Here, the die stretches the expansion element. However, it is also possible for the carrier surface of the expansion element to be pressed on the workpiece using compressed air or by the action of a vacuum.
In order to prevent the damage of delicate workpieces, in particular brittle and fragile workpieces of glass, glass ceramics or ceramics, during the printing process, the die face of the die can be made from an elastic, resilient material.
So that no coating material is spread between two printing processes, a cleaning arrangement is assigned to the transfer element, by which the carrier surface of the expansion element can be cleaned after the printing process.
It is also possible for the carrier surface of the expansion element to have a silicon coating or to be formed by silicon rubber. Such an embodiment of the surface prevents coating material from adhering to the carrier surface after the printing process.
If workpieces are continuously fed to the printing device, for example by a conveyor belt, the printing process can be designed so that the transfer element, which circulates as an endless tape, is routed past the expansion device. The endless tape can be stopped during the expansion of the carrier surface and the performance of the printing process. The conveyor belt can be stopped simultaneously with the cycling of the endless tape.
A continuous production process can be achieved if the transfer element circulating as an endless tape is conducted past the expansion device. During the extension of the carrier surface and the execution of the printing process the expansion device, and simultaneously the workpiece, are conducted along with the endless tape.
In one embodiment of this invention, a corona device is assigned to the expansion device, which causes or aids the transfer of the coating material to the printing surface of the workpiece to be imprinted.